Method and device for separating pipes or columns that are anchored into the ground The invention relates to a device and a method for separating upright pipes having their lower end anchored into the ground, particularly for support legs of an offshore oil drilling or oil supply platform.
To win the numerous crude oil reservoirs, drilling has been conducted for some time not only from oil fields accessible by land, but also offshore fields located under the ocean floor and other bodies of water. Such drills have been sunk at various water depths and, in part, far from the coast. In principle, the structure above the water surface, is the same drilling rig as is used on land, only on a supply platform positioned above the water surface. The type of support for the supply platform on the ocean floor is dependent, in part, on the water depth. Most offshore oil supply platforms are anchored into the ocean floor by means of support legs formed from large pipes.
Depending on the condition of the ocean floor, the support legs are embedded into the ocean floor, for example, rammed in or retained by the friction in the ocean floor. If this is insufficient, there is an alternative in which the embedded base of the support legs is installed in underwater cement or something similar, which also partially has an outlet in the surrounding ocean floor from the lower end of the pipe and which forms an artificially created ocean floor after hardening, the anchoring effect of which is contributed to by the effect of the weight of the cement, which fills up the lower part of the respective pipe up to a certain height. Using these measures, the supply platforms obtain stability under load even in problematic underground situations, which provide resistance to the platforms under the extreme loads in high seas.
The first of these platforms has operated in the North Sea for approximately 20 to 25 years. They are no longer needed in the meantime because the oil fields that were drilled with these platforms have been exploited. They cannot simply be left standing because they pose a hazard for ship travel.
Therefore, there is a need for a method and devices with which the oil supply platforms can be removed from the ocean after their service life has passed. While the removal of the structures of the platform and the platform itself are similar in principle to those used for land-based oil rigs, the support structures or platforms that are, in part, in deep and moving water, pose considerable problems. The support legs also need to be removed, but for the reasons indicated, cannot simply be cut off above sea level or just below the ocean surface, rather the specifications from the responsible authorities require that the support legs be cut off a section below the ocean floor.
From DE-PS 671 660, a device for cutting through pipes embedded in well drill holes is known, the cutting tool of which is lowered into the pipe to the separation point by means of a rod assembly. The cutting tool is used at the inside wall of the pipe and cuts through it from the inside to the outside.
This device is not suited for separating support legs of the platform indicated because the separation point is always in a region of the support leg that is filled with ocean floor matter, cement, and other things and thus does not permit lowering of the separation point.
Therefore, it was attempted to have diving teams dive to the ocean floor with suitable equipment and to cut the support leg from the outside using a diamond wire placed about the support leg driven in a longitudinal direction. Due to the large thickness of the pipe wall, this is a time-consuming and not necessarily non-dangerous process for the dive teams.